Neonate (< 24 h) larvae of the seabream, Sparus aurata, were exposed to sublethal concentrations (0.1-1.0 mg x L(-1)) of the anionic surfactant Linear Alkyl-benzene Sulphonate (LAS) for 72 h under laboratory conditions. The first histopathological changes, such as peri-yolk sac edema, were observed at concentrations of 0.2 mg x L(-1). Higher exposure concentrations provoked disorganisation of the nervous system, trunk musculature and trophoblastic sincitium as well as in the digestive epithelium. Immunohystochemical CYP1A analysis, however, was not shown to be an adequate indicator of sublethal effects produced by exposure to this type of anionic surfactant